A new Web site unveiled last week will track policies imposed by popular Internet sites such as Facebook and Google, hoping to help users spot potentially harmful changes.

TOSBack.org, the brainchild of privacy advocacy group Electronic Frontier Foundation, will track terms of service modifications within hours of an update.

The site will compare old and new policies side by side and highlight changes. With about two dozen sites covered already, TOSBack.org plans to add more agreements, from credit card, bank, cable TV and other companies.

Tim Jones, the EFF’s activism and technology manager, hopes the site will help avoid debacles such as the one faced by Facebook in February.

Changes to Facebook’s terms of use over control of content went unnoticed at first. But amid protests that Facebook might hold sway over content indefinitely, the company agreed to solicit user feedback. The site reverted to the previous terms of use policies as it tried to resolve the issues raised. Ultimately, Facebook let users vote on revised terms, which clarify that users own their information, not Facebook.

But Jones said many Web sites change their terms of service all the time and often don’t notify their users.

“Terms of service policies are obviously really important. They form the foundation of your relationship with almost every site you visit on the Internet,” he said. “But almost no one really has time to read them or the legal background to read them.”

TOSBack.org aims to make the general public more aware of user agreements and how it affects them, Jones said.